Numerous studies and publications have shown the benefits of automating window coverings and, in particular, it is well known that automated window coverings can greatly improve the energy efficiency of commercial buildings by reducing heating and cooling loads. These benefits can also extend to residential applications with the added benefits of enhanced security and convenience. The benefits of daylighting control, whereby daylight is harvested and augmented by artificial lighting when necessary are also known. However, the benefits of daylighting control systems have been shown to be highly dependent upon the efficacy of an automated window covering system that works in tandem with the daylighting control system.
Despite numerous designs and strategies that have been introduced at points in time over many decades, automated window coverings have not been implemented and installed in quantities that are commensurate with the perceived benefits of automated window coverings. This is due in large part to the limitations and relative high cost of existing, known prior art automated window covering designs. As an example, typically prior art automated window covering designs that provide the required robustness of design and functionality to achieve benefits are too expensive. The high cost of such automated window covering designs mean that they are unlikely to be implemented, due to the fact that a reasonable payback period cannot be achieved.
In general, there are two recognized types of window coverings: (i) roll shades (also known as rollershades), whereby a fabric is rolled around a motorized tube that when activated causes the fabric to ascend or descend covering a certain portion of the window completely; and (ii) slat based window covering devices, such as shutters and venetian blinds where actuation of an installed motor causes tilting of the slats to a particular desired angle. Some venetian systems may be motorized to achieve a lift function of the entire blind as well.
Rollershades are frequently considered less desirable for sunlight control or daylight harvesting than slat based window covering devices. Unlike slat based window coverings the transmissivity of the window cannot be evenly altered from 0 to 100% over the entire window surface when a rollershade is installed as a window covering. An installed rollershade renders a segment of the window, from top to bottom, opaque or virtually opaque (depending on the material from which the rollershade is formed). A rollershade that renders a segment of the window opaque has the result of creating 0% transmissivity for the covered portion of the window that is rendered opaque or virtually opaque, whereas the remainder of the window that is uncovered, and therefore not rendered opaque, remains in a state that is untreated and that has the result of 100% transmissivity.
The variance of transmissivity levels in a window that is covered partially by a rollershade can create an undesirable situation. For example, a rollershade that covers the upper portion of a window and therefore renders the upper portion of the window opaque or virtually opaque may leave a bottom portion, or segment, of the window uncovered and therefore the bottom portion may not be opaque. The result may be that full sunlight streams unimpeded through the bottom portion of a window despite the fact that the rollershade has been dropped to cover the majority of the window. This can lead to undesirable solar heat gains occurring through the uncovered portion of the window. Such a window covering may further cause a loss of opportunity for daylight harvesting through the covered portion of the window.
Slat based window covering devices, such as shutters and venetian blinds, may provide significantly increased flexibility for controlling the admittance of light more evenly over the entire window surface that rollershades.
Tilt only slat based systems may also provide a significantly simpler position control algorithm. Some complex tilt and lift systems for slat based blinds or shutters may contain dual motorization and control packages to perform the two disparate tasks of tilting and lifting. The lift function of such systems may add a significant cost to the system, and this cost may not be justified as it may not be commensurate with any payback or return on the investment in the installation of a tilt and lift system that is realized through the reduction of a building's energy consumption due to the installation of such a system.
Simpler control systems may contain no position feedback information. Such systems may rely solely on a user to time the energization of a motor until the desired slat rotation position is achieved. More complex control systems may utilize rotary encoders utilizing optical interrupters and opto-couplers. A significant drawback of such prior art systems is that they typically require calibration in situ, as well as periodic recalibration. Such systems may also suffer from drift.
Prior art systems may experience a loss of positional information during a power outage. Such prior art systems may require either battery backup, non-volatile memory, or recalibration upon powerup. Typically such systems may remain powered on constantly.
For example, prior art automated window covering systems, such as that described in U.S. Pat. No. 7,417,397, attempt to implement complex control algorithms that determine a roll shade position based on the time of year, geographical location, and orientation. Such systems are complex, and are often too expensive for home automation.
There are further drawbacks to prior art automated window covering systems which also attribute to the lack of widespread installation of such systems. One such drawback is that the efficacy of prior art automated window covering systems can be easily defeated. For example, prior art automated window covering systems may be defeated by reflected sunlight which is very common in high density urban centres.
Another drawback of prior art automated window covering systems is that although designs that are less expensive may be appealing from a price perspective, such designs frequently have limited functionality. The limited functionality of the prior art automated window covering systems has the result that such systems are deemed to be unsuitable for commercial operations. This is a significant drawback in that the bulk of the perceived benefits from the installation of automated window covering systems are considered to be in installation of such systems for commercial operations.
What is needed is an improved apparatus and system which addresses at least some of these limitations in the prior art.